Traction control systems, also known as anti-slip regulation (ASR) systems, are used on vehicles to prevent loss of traction of the driven wheels to maintain control of the vehicle and to prevent deterioration of the accelerating performance due to longitudinal slip of the driven wheels. Traction control is necessary, for example, when the driver applies the accelerator excessively and the condition of the road surface is such that the torque applied to the wheels causes them to slip.
Feedback control methods, which are typically employed, include monitoring wheel slip and detecting when it becomes excessive due to an excessive driving torque (e.g. sudden application of the accelerator pedal). After such a determination appropriate action may be taken, such as reducing the engine output or applying a braking force to the driven wheels. Traction control may be implemented within the engine control unit (ECU) of the vehicle to reduce engine torque by retarding or suppressing the spark to one or more cylinders of the engine, reducing fuel supply to one or more of the engine cylinders, closing the throttle, or, in turbo-charged vehicles, actuating the boost control solenoid to reduce boost and therefore engine power. Additionally, the wheel brake to one or more of the wheels may be applied to control wheel slip and transfer drive torque from a slipping wheel to at least one other which may be able to generate even greater traction forces.
Traction control systems are typically implemented in a vehicle as part of a stability control system (SCS) operable to enhance stability of a vehicle by detecting and reducing excessive wheel slip. If excessive wheel slip or vehicle instability associated with excessive wheel slip is detected while cornering, the stability control system may automatically apply braking to individual wheels or alter the powertrain torque output to assist a driver in steering the vehicle in an intended direction, for example around a corner.
The feedback approach used in existing SCS may not provide a fast enough response under certain driving conditions. For example the time required for the wheel slip measurements (or values) to be calculated and processed within the ECU and for an effective response to be implemented may be longer than the time it takes for undesirable effects resulting from wheel slip to occur, resulting in a missed opportunity to provide automated stability enhancements in a timely manner.
It is against this background that the present invention has been conceived. Embodiments of the invention may provide a method, a system or a vehicle that provide control over a rate that torque associated with a vehicle powertrain decreases to improve vehicle behavior. The rate control may be based on a request from the driver to decrease torque. The torque decrease rate may be kept within a range of a rate limit, which is dynamically variable depending on the current conditions, such as the driving maneuver the vehicle is performing.